This invention relates to sensors for measuring bioanalytes and to methods for making such sensors. More particularly, the invention relates to sensors for sensing lactate and to methods for making such sensors.
Lactate is a small molecule that is produced by all tissues and organs of a patient""s body that are in xe2x80x9cdistress.xe2x80x9d Wherever in the patient""s body the demands for oxygen exceed the supply, then a state of low perfusion exists and lactate is produced. For example, lactate is produced if a patient is bleeding, if a patient""s heart is failing, if a person""s limb is in danger of being lost, or if a person is not getting enough oxygen to breathe. Thus many life and limb threatening clinical states produce elevated blood lactate levels, even in the face of adequate oxygen delivery to the patient. It is a matter of oxygen supply and metabolic demand.
At the cellular level, lactate is inversely proportional to the vital cellular energy stores of adenosine triphosphate and is produced within six seconds of inadequate perfusion or cellular injury. It is thus an ideal biochemical monitor of cellular viability at the tissue level, and of patient viability at the systemic level.
Clinically, the dire significance of elevated and rising blood lactate values is known. Trauma physicians and clinical evidence support the hypothesis that a simple, inexpensive, continuous, monitor of lactate in the trauma setting, will save lives by providing timely, life-saving information that will help dictate triage and therapy. For example, an emergency room patient who has a blood lactate level of 4 mM has a 92% mortality rate within the next 24 hours. If this level is 6 mM, then the mortality rate rises to 98%. In animal experiments, blood lactate levels begin to rise within minutes of hemorrhage, and conversely, begin to fall just as quickly with adequate resuscitation. In multivariate analysis, blood lactate is the best indicator of the degree of shock (superior to blood pressure, heart rate, urine output, base deficit, blood gas and Swan-Ganz data) and is proportional to the shed blood volume. Blood lactate levels correlate with a trauma patient""s chances of survival. Therapy that fails to control a patient""s increasing lactate levels must be modified or additional diagnoses quickly sought.
Sensors have been developed for detecting lactate concentrations in a given fluid sample. For example, U.S. Pat. Nos. 5,264,105; 5,356,786; 5,262,035; and 5,320,725 disclose wired enzyme sensors for detecting analytes such as lactate or glucose.
One aspect of the present invention relates to a sensor including a bundle of electrically conductive fibers. The sensor also includes a sensing material coating at least some of the fibers in the bundle, and an insulating layer surrounding the bundle of electrically conductive fibers. The conductive fibers provide a large substrate surface area for supporting the sensing material. Thus, the sensor has a large surface area of sensing material even at small sizes. This large surface area of sensing material provides numerous advantages. For example, the large surface area assists in improving the response/sensing time of the sensor. Also, the large surface area assists in lengthening the useful life of the sensor.
Another aspect of the present invention relates to a method for making a sensor. The method includes applying a sensing material to a bundle of electrically conductive fibers. The method also includes covering the bundle of electrically covered fibers with an insulating layer after the sensing material has been applied to the fibers.
These and various other features which characterize the invention are pointed out with particularity in the attached claims. For a better understanding of the invention, it""s advantages, and objectives obtained by its use, reference should be made to the drawings and to the accompanying description, in which there is illustrated and described preferred aspects of the present invention.